Semiconductor dies are often attached to a substrate such as a leadframe, printed circuit board (PCB), etc. using a die attach paste such as an adhesive paste, a solder paste or a sinter paste. With thinner semiconductor dies, creepage of the die attach paste onto the top side of the die becomes more likely, which can result in electrical failure. In addition to avoiding such creepage, acceptable wetting between the back side of the die and the substrate also is important. Wetting refers to the flow of die attach material along x and y horizontal directions of the substrate. The better the wetting, the more easy the die attach process and the higher the probability to achieve a high-reliability level of the die attach during stress testing. Strong adhesion with an encapsulation material such as mold compound that surrounds the semiconductor die is yet another important consideration, especially at the top side of the die and at the inner leads before and after reliability stress testing.
Standard die attach processes which use conventional adhesive pastes, solder pastes and sinter pastes must be carefully controlled to avoid creepage of the die attach material onto the top side of the die during the die attach process, especially for thin dies. Standard die attach films can be used instead of pastes, where creepage is not an issue. However, die attach films are more expensive and have lower thermal and electrical performance as compared to adhesive pastes, solder pastes and sinter pastes. Further, another issue is to avoid voids.
Hence, there is a need for a low-cost die attach system with good wettability to the substrate and good adhesion with the die encapsulation material.